Conventionally, diamond tools such as a cutting tool and a wear-resistant tool have been made using a natural diamond or a diamond produced by the high pressure high temperature (HPHT) method. A natural diamond however exhibits large variations in quality, and cannot be supplied in a constant amount. A diamond produced by the high pressure high temperature method exhibits less variations in quality and can be supplied in a constant amount, but poses a problem that the cost for manufacturing facilities is high.
Another method of synthesizing a diamond is a vapor phase synthesis method such as a chemical vapor deposition (CVD) method. For example, Japanese Patent Laying-Open No. 2005-162525 (hereinafter abbreviated as PTD 1) discloses a diamond produced by the vapor phase synthesis method, which is transparent in an ultraviolet region and exhibits less crystal defects and strains. Furthermore, for example, Japanese Patent Laying-Open No. 2006-315942 (hereinafter abbreviated as PTD 2) discloses a diamond single crystal used in a semiconductor device substrate and exhibiting less strains. Furthermore, for example, Japanese Patent National Publication No. 2006-507204 (hereinafter abbreviated as PTD 3) discloses a CVD single crystal diamond material that is suitable to be used in an optical device or element. However, the diamond produced by such a vapor phase synthesis method poses a problem that chipping tends to readily occur when it is used for a tool material.